


Side-Effect

by gracerene



Category: Harry Potter - J. K. Rowling
Genre: Age Difference, Anal Fingering, Anal Sex, Aphrodisiacs, Background Relationships, Bottom Harry Potter, Casual Sex, Centaurs, Community: daily_deviant, Hogwarts, M/M, Mildly Dubious Consent, Mystical Creatures, Mythical Beings & Creatures, POV Harry Potter, Pining, Post-Hogwarts, Post-Second War with Voldemort, Pre-Draco Malfoy/Harry Potter, Professor Harry Potter, Sex Pollen, Sex with Sentient Animals, Smoking, Top Firenze, Tree Sex, Xenophilia, kind of
Language: English
Status: Completed
Published: 2019-07-09
Updated: 2019-07-09
Packaged: 2020-04-24 05:18:16
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,716
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/19166578
Author URL: https://archiveofourown.org/users/gracerene/pseuds/gracerene
Summary: Harry's all mixed up over his feelings for Draco, so Firenze offers him some mystical Centaur herbs to help grant him some clarity. Turns out these herbs have some… unexpected effects on humans.





	Side-Effect

**Author's Note:**

> Written for [Daily Deviant's July 2019 Themes](http://asylums.insanejournal.com/daily_deviant/752669.html): Magical Creatures (Centaur) & Sex Under the Influence
> 
> I'd say this is the most out-there thing I've written, but I once wrote [Sirius/Sirus's Motorbike](https://archiveofourown.org/works/5983170), so this is actually pretty on-brand for me. :D
> 
> Thanks so much to my betas for looking this one over for me! ♥

"I thought I might be seeing you tonight," Firenze said to Harry by way of greeting as he opened the door to his chambers.

They'd been colleagues for three years now and friendly—Harry wasn't sure if he could say they were precisely _friends_ —for nearly as long, so Harry was well-used to Firenze's cryptic way of speaking. He flashed him a weary smile as Firenze gestured him inside his forest-like rooms.

Immediately, some of the tension drained out of Harry's knotted muscles, the sensation of being outside—even if they were still technically indoors—helping to relax him. He loved Firenze's chambers, the wild forest-like nature of them, and he was thankful Firenze didn't seem to mind Harry barging in on him unannounced. In fact, he never seemed surprised whenever Harry turned up. Harry thought the stars surely had better things to do than let Firenze know when to expect visitors, but he wasn't going to complain about Firenze's easy hospitality.

"Since you were expecting me, I guess I don't have to worry about having interrupted anything?" Harry asked, sitting down on the soft carpet of moss that covered the centre of the room. He got comfortable and leaned up against what appeared to be a fallen tree trunk.

Firenze looked amused as he settled down near Harry, his legs folding neatly beneath his large body as he lowered himself to the ground. "You are correct. I am entirely free this evening and have plenty of time to hear about what ails you."

Harry snorted, tilting his head back against the log and gathering his thoughts as he stared up at the ceiling that, much like the Great Hall, mirrored the clear, star-lit sky outside. Firenze was a quiet, steady presence next to him, the silence surprisingly comfortable as he allowed Harry all the space he needed to process what was on his mind. 

If somebody had told him three years ago, back before he'd taken on the post of Defence Against the Dark Arts professor, that his closest confidant at Hogwarts would turn out to be _Firenze_ , he'd have laughed right in their face. Not that Harry had anything against the Centaur, but he'd always been a bit of an enigma—hardly an obvious candidate for a bosom buddy. Once Harry arrived at Hogwarts though, it quickly became clear that despite how welcoming all his new colleagues had been, it was _really_ bloody weird trying to befriend the professors who'd been teaching him less than a decade prior. His only real contemporary was Neville, but it had been more difficult for them to find time to hang out than Harry had expected. Neville was dating Hannah though, and was spending just about every free moment he had away from work down in London with her, and Harry couldn't begrudge him that. 

Firenze might have seemed like an unusual confidant in Neville's stead, but Harry liked that he treated him the same as he would any other person; he was neither deferential nor did he seem as if he was remembering the various shenanigans Harry had got up to as a student. There was something soothing about his presence and in the way he didn't feel the need to fill every silence with chatter. Somehow, over the course of the past three years, Harry had come to consider him a friend of sorts, even if their relationship was unlike any he had with his human friends. Harry had a feeling Firenze was lonely, given what had transpired between him and his herd, and Harry hoped he got some measure of comfort out of their interactions the way that Harry did. He'd certainly never turned Harry away, and he seemed pleased enough to while away an evening or two a week in Harry's company.

"It's nothing," Harry finally said with a sigh, still staring up at the twinkling stars. He could practically feel Firenze's steady, placid stare, and his cheeks warmed. "It's stupid," he clarified.

"Ah," Firenze replied as he began to rustle around for something in his satchel. "So it's about young Draco Malfoy then."

Harry's cheeks grew warmer as he fought the instinctive urge to deny it. He'd already spent such an embarrassing amount of time whinging about Draco to Firenze, that there was no use pretending that he wasn't still twisting Harry into knots. 

"He's just so _frustrating_ ," Harry growled, unable to contain his aggravation any longer. "One minute it seems like we're on the same page and the next he's colder than the Slytherin dungeons in winter. I don't bloody get it! I don't know where I'm going wrong."

Ever since Malfoy had partnered with Luna in producing _The Quibbler_ several years ago, he'd become a regular presence in Harry's friend group. Harry had _not_ been happy about it, and it had taken nearly a full year before he could even look at Malfoy without wanting to punch his face in. Eventually, Harry and Malfoy had formed a sort of truce that had led to a sort of friendship that had led to Harry sort of developing the world's most embarrassing pash on Draco Sodding Malfoy. That was bad enough, but worse still was that Harry couldn't tell if Draco felt the same way towards him. Sometimes he'd look at Harry like he wanted to eat him alive, but the moment Harry tried to indicate his interest, Draco would back off so quickly Harry was surprised he didn't trip over himself in his haste to put space between them. It was _infuriating,_ and that feeling was only exacerbated by the fact that, as a busy professor, Harry hadn't had time to pull in _ages,_ and he was getting bloody sick of only having his right hand, and a couple of choice toys, for company. He wanted to get _fucked,_ preferably by somebody other than himself. Preferably by _Draco,_ if he was even interested.

Firenze paused in packing his pipe, tilting his head as he looked at Harry with those astonishingly blue eyes that seemed to pierce right through to Harry's soul. "You're having trouble seeing things clearly. Perhaps you could use some help."

Harry sighed. "Yeah, I suppose so. There's so much shit between Draco and I… it's kind of hard to detangle it all."

Firenze nodded. "The Centaurs have long used certain herbs to help us in reading the stars and to aid us in working through our own private battles." He held up his pipe. "Perhaps you'd like to join me tonight and see if they provide you any insight."

Harry couldn't hide his surprise. Firenze might not hate wizards the way so many of his kind did, but he was hardly one to hand out the secrets of his kin. That he was offering to share this with Harry was a huge mark of respect. He wasn't sure how much help a handful of herbs would be in figuring out where he stood with Draco, but he certainly wasn't going to decline such a generous offer. Besides, at this point, Harry hardly thought it could _hurt_ matters either. 

"Sure, why not," Harry replied. 

Firenze nodded and finished packing the ornate pipe before cupping his hand over the bowl and igniting the herbs in an even light. He took a few long drags, the thick smoke curling out of his mouth like branches from a tree, before he passed the pipe over to Harry. Harry could count the number of times he'd smoked before on one hand, and he tried not to feel intimidated as he wrapped his lips around the stem and inhaled slowly. 

The smoke was sweet and earthy as it slid across his tongue, tasting vaguely of mallowsweet and sage and half a dozen other subtle flavours that Harry couldn't identify. The concoction was so smooth, Harry didn't even make a fool of himself and start coughing as the smoke slid into his lungs, his body tingling pleasantly as the effects slowly dispersed through his veins. He took a few more tokes and then passed the pipe back to Firenze, leaning back against the log and waiting for sudden clarity to hit him. 

Harry didn't feel as if he was being blessed with any particular mystical insight, but he _was_ feeling quite warm, his blood heating up inside him, pushing molten lava throughout his limbs. It was a liquid, languid kind of heat that glowed from within, pulsing hotly with each pump of his heart, throbbing as the blood circulated through his hardening cock. He blinked slowly as need bubbled up within him, a desire to touch and be touched tingling across his skin. If he thought he had the horn before, it was _nothing_ compared to how he felt now, like the very reason he was put on this earth was to be fucked. _Hard._

Images of Draco flit through his head: the flash of his white-blond hair, the sharp cut of his jaw, the amused curl of his lips, and his penetrating grey gaze. Harry couldn't suppress a moan as he imagined what it would be like if Draco were here right now and they didn't have all the awkwardness between them, how it would feel to have Draco on top of him, pressing him against the mossy ground. But Draco _wasn't_ here, and Harry had no bloody clue where they stood, or if he'd even be interested in what Harry was currently desperate to offer.

Harry's head lolled to the side, and he watched as Firenze took another hit from his pipe, his head tilting back as delicate flowers of smoke bloomed from his mouth. The silver-blond of his hair gleamed in the enchanted moonlight, and Harry couldn't help but note the striking similarity to the _other_ blond who had captured so much of his attention as of late. Like Draco, the bright hair suited Firenze, accentuating the blue of his eyes and the handsome lines of his face. He might not be human, but that hadn't stopped Harry from recognising how fit he was, with his defined chest and thick biceps and powerful body. It wasn't as if he was some dumb animal—Firenze was every bit as sentient as any of the humans Harry knew, and quite a bit smarter than most of them. Harry had hardly been the only one to take note of Firenze's good looks, either—every year there was a group of students who seemed to form an unofficial fan club for the Divination professor (or one of the Divination professors, anyway), following him around with hearts in their eyes.

But all of Harry's casual appreciation of Firenze's good looks had never made him feel like this before, never made him desperate to lick the salt from Firenze's throat, or made him wonder what it would be like to be speared on Firenze's cock. Another wave of heat washed over him at the thought, leaving him panting and writhing, and when he opened his eyes, he met Firenze's startled gaze.

Firenze breathed in deep, his nostrils flaring as fire sparked white-hot in his crystal blue eyes. He was _smelling_ Harry, and the knowledge just made Harry's blood burn hotter. 

"I think I may have made a… miscalculation in offering you these herbs."

Harry shuddered as Firenze's soothing baritone vibrated through his body like the rumble of thunder during a storm. His cock throbbed, pushing against his tight denim jeans. "You think?"

Firenze's expression twisted into some strange cross between apology and need. "I did not anticipate that the effect would be so much different for wizards. I apologise for my misstep, and for any discomfort you might be currently experiencing."

Harry pushed himself up into a sitting position and faced Firenze, his breath laboured from the effort and from the arousal threatening to overwhelm him. "How sorry are you?" Harry asked. He licked his lips, and his stomach clenched when Firenze's keen eyes followed the motion.

"Hmm?"

Harry grinned and shuffled closer. "Sorry enough to help burn off some of this _discomfort?_ " 

Firenze blinked and cocked his head. "You wish to mate with me?"

A sharp laugh burst from Harry's throat. "Not how I would have put it, but I guess you're not wrong."

Firenze's gaze slid down Harry's body, appreciative and assessing. "You are quite attractive, for a human, and the way you smell right now… If you are certain—"

That was good enough for Harry. Without waiting for Firenze to finish his sentence, he pushed forward the last few inches and joined their lips in a heated kiss. 

Whatever was in that herb concoction Firenze had given him had clearly magnified his senses, because Harry didn't think anything had ever felt as good as Firenze's mouth sliding against his own, his skilled tongue pressing between Harry's lips with surprising finesse. Harry couldn't stop himself from burying his hands in Firenze's hair, the strands like gossamer silk filtering between his fingers. He pushed himself close, as close as he could get, moulding his body against Firenze's broad, bare chest, the skin burning hot through Harry's shirt. Even the smell of him seemed intensified in Harry's feverish state, an earthy, spicy musk that filled Harry's nose, more intoxicating than Amortentia. 

He was panting like he'd just run several miles by the time he pulled away from Firenze, noting with pleasure that he clearly wasn't the only one affected. Firenze's breathing might be steady, but his eyes were dark and predatory, and when he pushed himself off the ground to tower over Harry, Harry saw even further proof that Firenze was most definitely enjoying himself. 

Harry's mouth watered as he took in the long, thick length of Firenze's erection where it hung between his hind legs, flushed and dripping. He was hung like… well, like a horse, and Harry's entire body _burned_ with the need to feel Firenze deep inside him, splitting him open. 

"You are eager for it, aren't you?" Firenze said thoughtfully, and Harry shudder at the tone. "Such a fascinating side-effect."

"Yeah, fascinating," Harry replied absently, the majority of his focus still centred on Firenze's magnificent cock as he tried to figure out the best way to get it inside him as soon as possible. He met Firenze's gaze. "So how do we do this?"

Firenze smiled serenely, the look at strange odds with the throbbing erection indicating his current state of arousal. He gestured at the higher end of the log that Harry was currently leaning against. 

"If you bend over there, that should do quite nicely."

"Done this before?" Harry teased as he stood up and kicked off his jeans and pants, leaving on his shirt to help protect his skin from the rough bark. The last thing he wanted to deal with while getting fucked over a tree was a splinter.

Firenze quirked a brow. "I have always had an interest in humans," he said, as if that was an answer to the question. Harry shivered. He supposed it was.

Still, Harry wasn't sure just _how_ familiar Firenze was with fucking wizards, and he figured it was best not to take any chances. He grabbed his wand and cast a stretching and lubrication spell before bending over the log and exposing himself completely to Firenze's hot gaze. Harry wasn't a fan of the spells generally speaking, but they had certainly come in handy a time or two, and he didn't think he currently had the patience for a more manual approach. Given that the desire to be filled felt like an actual physical need at that particular moment, he was grateful for anything that might expedite the process. 

He could hear Firenze moving closer, the sound of his hooves against the mossy floor so much different than human feet. The knowledge that Firenze _wasn't_ human and was still about to fuck Harry right over this log shouldn't have made Harry even harder, shouldn't have made him cant his hips back in eager supplication, and yet… Fuck, he was just so empty, so needy and desperate to be filled that when Firenze sunk two of his fingers deep into Harry's arse without so much as a warning, Harry almost came on the spot.

"Oh, _fuck_ ," Harry moaned as Firenze rubbed his fingers along Harry's inner walls, finding his prostate with ease and massaging the bundle of nerves until Harry thought he'd shake right out of his skin. It felt unbelievably good, better than anything he had ever felt in his entire life, but still he wanted more.

"I'm good, I'm good," Harry panted, clenching down on the thrusting fingers. " _Merlin,_ just fuck me already."

Firenze hummed as he pulled his fingers out of Harry's arse. "If you insist."

There was shuffling behind him, and then Firenze's forelegs were stepping up onto the sturdy log, one on either side of Harry's splayed body. His stomach flipped as he took in the golden coat that trailed down Firenze's legs, fading into pale cream, the same shade as the fair hair on Firenze's head. It was surreal, looking at the hooves next to him while something thick and hard began to nudge between his arse cheeks and press inside.

Harry gasped and panted as the thick length of Firenze slid in, inch by inch, longer and thicker and _bigger_ than anything he'd ever taken before. He had the vague thought that it should probably hurt, being fucked by something so monstrous, but all he felt was bliss and desire, the herbs relaxing his body and heightening every pleasure centre he possessed. There was the faintest hint of burning ache, but mostly all he felt was full. Full, and taken, and so fucking good, especially when Firenze sunk all the way inside, Harry's arse nestled up against his groin while short, coarse horse-hair scratched against his arsecheeks.

After that, things grew a bit hazy, all rational thought flying straight out the window as Harry was reduced to base feeling and need. All he knew was the white-hot pleasure plunging in and out of his arse with firm, steady thrusts. Fire licked across his skin, pooling in his groin as pressure built inside of him with every brush of Firenze's fat cock against his prostate. Harry wasn't sure what finally pushed him over the edge—he wasn't quite cognisant enough for that—but he _was_ aware enough to take note when the pressure inside of him finally exploded outward, liquid euphoria flooding through his veins as his cock erupted thick streams of white against the side of the log.

Firenze wasn't far behind him, thrusting several more times before letting out a sound that was suspiciously close to a neigh as a heavy pressure flooded his arse. Gently, Firenze eased out, making way for what felt like half a gallon of come to leak out of Harry's relaxed arsehole. He could feel how open he still was, loose and lax from the memory of Firenze's cock. Its absence left him strangely bereft, and he reached for his wand, cleaning himself off as best he could before tugging up his pants and jeans.

Harry could still feel the heady effects of the herbs floating around in his system, making him sensitive and oddly buoyant, but the all-encompassing need seemed to have burnt off with his orgasm. There was still some part of him, though, that craved touch, and he shivered even in the relative warmth of the room. He wasn't really sure what came next, and though he could tell that the orgasm and the herbs were allowing him to be far more mellow about what had just happened than he'd be otherwise, he still didn't know what the proper protocol was for the aftermath of herb-induced casual sex with a not-entirely-human colleague.

Thankfully, Firenze didn't seem to have similar hang-ups, apparently completely unconcerned with their unexpected coupling. 

"You're welcome to leave, if you'd like," Firenze said as he gracefully eased himself to the ground, clearly making himself comfortable. "But I'd prefer if you'd stay, at least until the effects of the herbs have worn off completely."

"Offering your stud services?" 

Firenze's expression was placid, though Harry saw a hint of amusement flickering in his eyes as he inclined his head. "If necessary."

Harry sighed and flashed him a tired smile. "Yeah, all right then."

He Conjured up a blanket, hesitating for only a moment before boldly making his way to Firenze's side. Harry curled up against his broad, golden body, soaking in his inhuman warmth while Firenze lit another pipe, silence hanging comfortably between them.

The whole night still seemed so surreal, the strange effects of the herbs making his sensitised body feel almost foreign. He glanced over at the log next to them, the one he'd just been bent over as he'd begged Firenze to fuck him. God, he'd needed that, had needed to let off a little steam, to be fucked into an orgasm intense enough to clear out all the noise in his head. Hell, that was why he'd taken those freaky herbs in the first place, to try and gain a little clarity and perspective about the whole Draco situation. Draco who, even now, completely fucked-out as Harry was, _still_ made his stomach wriggle in a not-entirely-unpleasant way. Yeah, Draco had been running hot and cold worse than a broken faucet, but it wasn't as if Harry had been all that clear about what he was after, either. He could hardly blame Draco for being wary given their history. He'd been tying himself in knots over Draco for months when all it would really take to straighten himself out would be to make a bloody move and ask Draco out already. One way or another, he'd get an answer to the giant question mark that was his and Draco's current relationship. He knew what he _wanted_ the answer to be, but it was the uncertainty and not knowing that had been driving him up the wall.

Harry grinned as he closed his eyes and let the steady rise and fall of Firenze's belly lull him to sleep. It might have been a little unorthodox, but it appeared the secret Centaur blend of herbs had worked their magic after all. 

He'd Floo Draco in the morning.

**Author's Note:**

> [Kudos ♥] and [Comments] are fabulous! I'd love to hear what you think!
> 
> Come find me on [tumblr](http://gracerene09.tumblr.com/)!


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